This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Children with symptomatic asthma have improved asthma control with medical treatment of esophageal reflux with the proton-pump inhibitor, lansoprazole, as compared to children treated with placebo. This will be a multi-site, randomized, double-masked, placebo-controlled, parallel group clinical trial. Three hundred children will be randomly assigned to one of two treament groups: oral lansoprazole or oral placebo for 24 weeks. The primary outcome measure is a significant change in the ACS during treatment. Secondary outcomes include lung function, episodes of poor asthma control, asthma symptoms, asthma-related symptoms will be evaluated by esophageal pH monitoring in a subset of participants prior to randomization. GERD severity, frequency, and relationship to asthma symptoms will be evaluated by esophageal pH monitoring in a subset of participants prior to randomization. V1 is the screening visit, V2 is the randomization visit, V3 is an interim phone visit, and V4-V9 are monthly data collection visits. Participants will be asked to record daily asthma symptoms, daily morning peak expiratory flow, awakenings at night because of asthma, asthma treatments, and healthcare use. Participants will complete questionnaires concerning health and asthma history, asthma symptoms and daily activities, quality of life as it relates to the subject's asthma, and stomach symptoms. Lung function tests include methacholine challenge, spirometry, exhaled breath condensate, and nitric oxide. The optional acid reflux test is a 24 hour pH probe where the participant will have a probe/tube inserted through the nose and down into the stomach to measure acid outcome. There will be 2 blood draws, one to test study drug level, and the second for DNA analysis. The subject will be assigned to take either lansoprazole, a proton pump inhibitor, or placebo on a daily basis for 24 weeks.